Rotor structure and method of broaching the same

ABSTRACT

A method of broaching axial grooves for blade roots in a turbine rotor structure for a marine turbine having forward and astern elements exhausting to a common outlet and simultaneously broaching axial grooves for an integral exhaust baffle structure. The resulting structure is a rotor having a plurality of axial rows of grooves comprising an equal number of grooves in the rotor portion and the baffle structure.

United States Patent Ortolano 1 Oct. 24, 1972 [54] ROTOR STRUCTURE AND METHOD 1,287,020 12/1918 Hinscin........................4l5/99 0F BROACHING THE SAME l.3l0,680 7/l9l9 Sherbondy.................4l5/l02 [72] Inventor: Ralph J. Ortolano, Palos Verdes FOREIGN PATENTS QR ppuc 'no s Peninsula, Calif.

899,507 6/1962 Great Bntaln ..4l5/ 102 [73] Assignee: W Electric Corporation,

Pittsburgh, Primary Examiner-C. .l. Husar 1 Attorney-A. P. and Cristiano, Jr. [2i] Appl. No.: 111,530

[57] ABSTRACT [52] US. Cl. ..4l6/199, 415/99, 415/102, A method of breaching axial grooves for blade roots 416/219 in a turbine rotor structure for a marine turbine hav- [51] Int. Cl ..F0ld 5/06 ing forward and astem elements exhausting to a com- [58] Field of Search ..4lS/99l02; mon outlet and simultaneously breaching axial 416/199; 60/102 grooves for an integral exhaust baffle structure.

The resulting structure is a rotor having a plurality of [56] References cued axial rows of grooves comprising an equal number of UNITED STATES PATENTS grooves in the rotor portion and the baffle structure.

979,518 l2/l9l0 Larrabee ..4l5/l02 5Claims,3Drawing Figures minimum: .912 3 700-353 sum 2 or 2 \Killlllllil WITNESSES INVENTOR 3 5 /X,w }M Ralph J. Ortolono ROTOR STRUCTURE AND METHOD OF BROACHIN G THE SAME BACKGROUND OF THE INVENTION In turbines for driving ships and particularly with steam turbines, it is known to use a relatively large power turbine for propelling the ship in a forward direction and a separate turbine of relatively smaller power for reverse of astem movement, the two turbine elements generally being located on the same drive shaft and within the same housing. Both the forward and reversing turbine elements usually exhaust the spent steam to an exhaust which is common to both turbines. Hence, a bafile structure is provided to prevent steam from the reversing turbine from impinging on the forward blading in the low pressure end during a reversing operation, and correspondingly to prevent the steam from the forward turbine from impinging on the reverse turbine blading during forward operation.

What is desirable then, is to provide a baffle structure which is effective to substantially prevent spent steam from interacting in either the forward or reverse turbine directions and to more economically machine the baffle structure to provide a substantial saving in time and money in the construction of the turbine rotor structure.

SUMMARY OF THE INVENTION The following disclosure relates to a multi-stage axial flow marine turbine and more specifically to a structure and method of broaching the rotor and baffle structure therein.

The marine turbine rotor structure has a plurality of stages of turbine rotor blades for the forward turbine elements and a smaller plurality of rotor blades for the reverse turbine elements, the two turbines being separated by a baffle structure as well known in the art. In breaching the rotor structure the angle of attack or of reciprocation of the cutting tool is either parallel to or inclined relative to the periphery of the rotor structure and axially extending grooves are simultaneously cut in the rotor and the baffle portion. The method of inclining the angle of reciprocation is more fully shown and described in application Ser. No. l I 1,531 by A. H. Redding and is assigned to the present assignee.

By using this broaching method, a rotating baffle structure can be provided at a substantial saving in time and cost, since the root structure for the baffle is broached simultaneously with the root structure for the rotor, where simultaneously is defined as machining the grooves together at substantially the same time.

The resulting structure is a rotor having a plurality of axial rows of grooves which are similar in shape, comprised of equal numbers of annular grooves in the baffle structure and the rotor structure.

DESCRIPTION OF THE DRAWINGS FIG. I is a longitudinal view, partly in axial section, of a marine turbine having a rotor structure formed in accordance with the principles of the invention;

FIG. 2 is a view taken along lines Il-II in FIG. 1; and

FIG. 3 is a view taken substantially along line III-III in FIG. I with a portion of the blades removed for clarity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, and in particular, to FIG. 1, there is shown a representative marine turbine propulsion plant 10. The turbine propulsion plant 10 for a ship comprises a forward turbine element 11 for driving the ship ahead, and a reversing turbine element 12 for driving the ship astern. The forward and reversing turbines 11 and 12 have casing portions 14 and 15 respectively, to which the stationary blading 17 of the forward turbine 1 1 and the stationary blading 18 of the reversing turbine are secured to the inner wall portions thereof. The stationary blades 17 and 18 comprise a plurality of annular rows of equally spaced blades. Rotating blades 20 and 21, corresponding to the forward and reversing turbines 11 and 12, respectively, are secured to a common rotor structure 23, which rotor is coupled by any suitable means to the propeller shaft of a ship, not shown. The rotating blades 20 and 21 form a plurality of annular rows of equally spaced blades, the stationary blades and the adjacent rotating blades jointly defining a stage. As shown, the forward turbine 11 and the reversing turbine 12 have ten and three stages, respectively.

Hot motive steam for driving the rotor structure 23 by the forward turbine 11 in one direction, is introduoed through a steam inlet 25, which is in fluid communication with the forward turbine. After the steam expands through the various stages of the forward turbine 11, it exits through a discharge passageway 27, as indicated by the arrows A, moving from right to left. Hot motive steam for driving the reversing turbine 12 in the opposite direction is introduced through a second steam inlet passage 29 and is expanded through the various stages in the reversing turbine, and exits into the common discharge passageway 27 as indicated by the arrows B from left to right. Obviously, hot motive steam is introduced to only one of the turbines at a time.

As previously explained, a baffle structure 31 is used to prevent spent steam, from either the forward or reversing turbines 11 and 12, from impinging on the rotor blades, 20 and 21 respectively, in the last blade row of the other. The principle object of the present invention is to design the turbine so that an efficient and inexpensive baffle structure can be used to effectively prevent the spent steam from interacting with the opposed turbine. The baffle structure 31 shown is of the rotating type which is secured to the rotor structure 23, rather than a bafl'le of the stationary type which is secured to the casing structure.

The bafile structure 31 is circular in shape and comprises a radially extending annular land portion 32, integral with the rotor structure 23, and a plurality of radially extending baffle segments 34 carried by the land portion. The baffle segments 34 have root portions 35, which as best shown in FIG. 2, are of fir tree root cross section and are of the side entry type. The bafile segments 34 are disposed in grooves 36, of corresponding fir tree cross section, in the land portion 32 of the rotor 23. The bafile segments 34 have plate portions 38 integral with the root portions 35. Opposing sides 38a of the plate portions 38 abut the sides of the adjacent plate portions to jointly form a continuous annular ring-like structure. The baffle land portion 32, the root portions 35 of the baffle segments 34, and the plate portions 38 cooperatively define baffle structure 31.

One proposed method of machining a rotor structure having a bafile 31 is to employ a broaching technique as more fully shown and described in a copending application of AH. Redding, Ser. No. 1 11,531, filed Feb. l, 1971, and assigned to the present assignee, wherein the angle of reciprocation of the cutting tool 30 (FIG. 3) of the broach is inclined to the periphery of the rotor structure. The cutting tool 30 is moved into engagement with the land portion 32 of the baffle 31 and cuts and axial groove 36 therein. The broaching continues and the tool engages the lands of the forward driving turbine 11 to cut an axial row of grooves 41 (FIGS. 1 and 3) in the rotor structure 23. As shown in FIG. 1, the grooves 36 in the baffle structure 31 and the grooves in the low pressure end of the turbine 11 are progressively smaller as they approach the high pressure end, indicating that the broaching tool is moving from right to left as taught by Redding. Furthermore, the grooves 36 are similar in shape. Depending on the shape, pitch, height and gauging of the annular rows of blades, some rows in the lands 40 of the forward turbine 11 may be incompatible with the axial row of grooves 41 and the diameter of the lands 40 in those rows, from the axis of rotation of the turbine, may be reduced to permit the breach to pass over them.

It is further noted that there are a plurality of axially extending rows of grooves 41 made up of the grooves 41a for the rotating blades 20 in the forward turbine l l and the grooves 36 for the baffle segments 34 of the baffle structure 31. It will be additionally noted that the land portion 32 of the baffle 31 must be at a compatible diameter relative to the diameter of the corresponding lands 40 of the forward turbine so that this broaching technique can be used.

Another proposed method of machining the rotor structure with a baffle structure 31 is to employ a broaching technique commonly known as through broaching." With this method, the path of the cutting tool is parallel to the centerline of the rotor, with the result that all of the ahead stages, the baffle, and the astern stages, as long as they have the same common maximum diameter, will have roots that are identical, both in shape, size and number. Of course, any stage, including the baffle, that has a diameter smaller than this maximum diameter, could have any type of root, including T roots, machined on it.

As best seen in FIGS. 1 and 3, the steam from the forward turbine, indicated by the arrows A exits from the last stage and strikes the baffle structure 31. The steam is then directed through the discharge passageway 27. On the outer extremities of the last row of rotation blades 20, the spent steam may strike the discharge passageway 27 directly, and then exit through passageway 27. Correspondingly, the steam from the reversing turbine 12, indicated by arrows B, exits directly into the passageway 27 along the slope portion 42 of the passageway or strikes the baffle structure 31 and then exits into the passageway. Therefore, both blade rows of the forward and reversing turbines 11 and 12 are protected.

It can be seen, therefore, that a rotating baffle structure can be manufactured efficiently and effectively by a continuous broaching technique, thereby eliminating the higher cost machining processes previously employed. The grooves 36 for the root portions 35 of the baffle structure 31 are preferably broached simultaneously with the grooves 41a in the turbine rotor 23 without any additional cost, since the broach passes over the land portion 32 of the baffle structure 31 during the same pass.

Although only one embodiment has been shown, it will be obvious to those skilled in the art that certain modifications may be made be made within the scope of the disclosure. As an example, although blades hav ing fir tree roots have been shown, other blades having roots of side entry shape may also be used, and although the rotor has been shown to be a solid rotor, the rotor structure could be a plurality of discs fastened by any suitable means. Therefore, it is intended that all the matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A multi-stage rotor structure for a marine turbine unit comprising:

a forward turbine element, rotatable in one direction, and a reverse turbine element rotatable in the opposite direction, both elements being secured to said rotor,

a baffle structure disposed between said driving and reversing turbine elements and secured to said rotor,

said forward turbine element comprising a plurality of annular lands,

each of said lands defining an annular array of equally spaced and axially extending grooves,

a plurality of rotatable blades having roots of the side entry type disposed in said grooves,

said baffle structure comprising an annular land portion and segmented portions;

an array of equally spaced, axially extending grooves defined in said land portion,

said segmented portions being disposed in said grooves in said land portion,

and said grooves in said baffle structure and said grooves in said rotor structure being equal in number and axially aligned to cooperatively form a plurality of axial rows of grooves.

2. The structure recited in claim 1 wherein the grooves in the rotor structure which are aligned with the grooves in the baffle structure are grooves for the rotatable blades of the forward turbine element.

3. The structure recited in claim 1 wherein the segmented portions of the baffle structure are comprised of root portions and plate portions, said root portions being disposed in the grooves in the land portion of the baffle structure, and said plate portions extending radially outward from the land.

4. The structure recited in claim 3 wherein the root portions are of fir tree cross section and are of the side entry type.

5. The structure recited in claim 3 wherein the plate portions are integral with the corresponding root portions and the opposing sides of the adjacent plate portions fricu'onally abut the sides of adjacent plate portions to jointly form an annular ring structure to help prevent spent steam from the forward and reversing turbine elements from impinging on the opposing turbine element.

t I t l 

1. A multi-stage rotor structure for a marine turbine unit comprising: a forward turbine element, rOtatable in one direction, and a reverse turbine element rotatable in the opposite direction, both elements being secured to said rotor, a baffle structure disposed between said driving and reversing turbine elements and secured to said rotor, said forward turbine element comprising a plurality of annular lands, each of said lands defining an annular array of equally spaced and axially extending grooves, a plurality of rotatable blades having roots of the side entry type disposed in said grooves, said baffle structure comprising an annular land portion and segmented portions; an array of equally spaced, axially extending grooves defined in said land portion, said segmented portions being disposed in said grooves in said land portion, and said grooves in said baffle structure and said grooves in said rotor structure being equal in number and axially aligned to cooperatively form a plurality of axial rows of grooves.
 2. The structure recited in claim 1 wherein the grooves in the rotor structure which are aligned with the grooves in the baffle structure are grooves for the rotatable blades of the forward turbine element.
 3. The structure recited in claim 1 wherein the segmented portions of the baffle structure are comprised of root portions and plate portions, said root portions being disposed in the grooves in the land portion of the baffle structure, and said plate portions extending radially outward from the land.
 4. The structure recited in claim 3 wherein the root portions are of fir tree cross section and are of the side entry type.
 5. The structure recited in claim 3 wherein the plate portions are integral with the corresponding root portions and the opposing sides of the adjacent plate portions frictionally abut the sides of adjacent plate portions to jointly form an annular ring structure to help prevent spent steam from the forward and reversing turbine elements from impinging on the opposing turbine element. 